A spiral pump with rotating displacement disks is known from German Patent Document DE-C-2603462, FIG. 5. It is distinguished by a nearly pulsation-free conveyance of the gaseous working substance, comprising air or an air-fuel mixture, for instance, and can thus be used advantageously for charging purposes in internal combustion machines. During operation of such a compressor, a plurality of approximately sickle-shaped work chambers are enclosed along the pumping chamber, between the spiral-shaped ribs. They move through an inlet and to an outlet, in the course of which their volume is steadily reduced and the pressure of the working medium is correspondingly increased. With these spiral compressors, the conveyed quantity at a given volumetric efficiency and the maximum boost pressure are defined by the transmission ratio; in particular the inner pressure ratio is fixedly defined because of the spiral geometry selected. In this known machine one displacement disk is seated on an axle journal. The second disk is connected to a drive shaft in a manner fixed against relative rotation. When the first disk rotates, the second disk is carried along in the same direction of rotation and at the same rotation speed. In the process the two disks execute a relative motion in the form of a circular displacement.
Another charger of this type is known from Swiss Patent Document CH-A-501 838. In this case the variant shown in FIGS. 6 and 7 is a multicycle, single-step machine. One of the two rotating disks is connected to a central drive shaft. During rotation of this one disk, the second disk is carried along in the same direction of rotation via the spiral-shaped ribs by means of a transmission of force. The stationary axle on which the second disk is seated is hollow for the purpose of guiding the working medium to be conveyed out of the machine. These multicycle machines have the advantages that each displacement disk is completely counterbalanced individually, and that a more uniform, nearly pulsation-free conveyance is possible. In addition, the radial displacement of the two disks and thus the eccentricity between the two rotating shafts is less than in single-cycle machines, which leads to lower slip speeds between the spiral-shaped ribs. In principle, therefore, this type of compressor can be operated at higher rpm.
Another multi-step spiral pump is known from this same reference. However, it is a single-cycle machine that furthermore does not operate rotatingly, but with orbiting spiral ribs; that is, they are stationary on one side. Because in multicycle machines an interior compression is effected between the work chambers, which are disposed one behind the other, special arrangements must be made for the conveyance of non-compressible media, such as liquids. In conveying compressible media, the rising temperature in the downstream work chambers is problematic.
An object of the invention is to create a spiral pump of the type mentioned at the outset, with which high pressures can be attained and with which the tolerance problems caused by temperature as a consequence of varying thermal expansion can be controlled.
This object is attained in accordance with the invention in that cooling means are provided in the intermediate chamber between the outlet of the radially outer step and the inlet of the radially inner step.
The spatial separation of the steps is a simple means for distributing the pressure reduction over the various steps depending on use; the available spatial conditions on the displacement disks can thus be put to optimum use. Through the cooling means provided in the space between the outlet of the radially outer step and the inlet of the radially inner step, the compression heat that has built up to this point can be dissipated. In a first embodiment of the invention, the cooling means can be ribs over which the flow takes place and which extend spirally on one of the displacement disks in the space. Alternatively, the space between steps can be formed with an outwardly positioned box through which the flow passes, the box being open to facing sides of the displacement disks, and extending outwardly on the sides of the displacement disks facing away from each other, wherein this box is provided on its outer walls with cooling fins.
It is advantageous that the sides of the displacement disks facing away from each other are provided with ventilating blades. This measure permits cooling of the displacement disks and, upstream of them, the bearing sections of the machines.